Many hazardous wastes have been disposed of improperly during the years since the chemical age began. Some of these resulted from incomplete reactions at chemical manufacturing plants; others were isomeric or side-reaction products which were not suitable for use. Still others are compounds which had been manufactured and in use, but had been discovered to present a real or potential hazard to workers in the plants manufacturing them, to their users, or to people exposed to them. Little notice was paid these discarded materials until recently, when the magnitude of their quantity has made it a problem which can no longer be ignored. Many were buried in improperly secured landfills; some in open dumps; some simply left standing in drums; some dumped on the ground.
Some companies early in the "waste mangement" business charged generators for disposing of their wastes, and merely stockpiled them, without making any attempt to effect a proper, environmentally safe treatment or disposal. Thousands of these dumps are known to exist, and much attention is being given to methods of containment or disposal of their contents. More recently, much effort has gone into devising processes for their destruction or disposal.
Methods for their disposal include: secured landfills; incineration in lime or cement kilns; incineration in specially constructed incinerators designed to retain the combustion gases for long periods of time in order to insure complete oxidation; oxidation in molten salt baths which utilize the molten salt to retain the combustion products and maintain the high temperature necessary. Recently adopted processes involve reaction of polychlorinated biphenyls (PCB's) with a sodium alkyl, a process which has been in use for a long time as an analytical tool. This is a reductive process in which the sodium in the sodium alkyl abstracts the chlorine from the PCB molecule. This can result in addition of the alkyl to the biphenyl ring structure, or it may be done in a medium which can supply substituents to the fragments.
Sodium metal has also been applied to the analytical determination of organically bound halogens; reducing the covalently bound halogen and forming the negative halide ion.